Justin's answer tells you how to raise the number of open files available total to the whole system. But I think you're asking how to raise the per-user limit, globally. The answer to that is to add the following lines to /etc/security/limits.conf:

* soft nofile 2048
* hard nofile 2048

(Where the * means all users.)

There's some summary documentation in that file itself and in man limits.conf. This is implemented via the pam_limits.so module which is called for various services configured in /etc/pam.d/.

And, I have to admit, I have no idea where that 1024 default comes from. And believe me, I looked. I even tried without the pam_limits module configured, and it's still there. It must be hard-coded in somewhere, but I'm not exactly sure where.